Nature of Operations and Summary of Significant Accounting Policies - Interest Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Interest costs charged to expense	$ 1,184	$ 1,294	$ 534
Plus: Interest cost capitalized	293	198	297
Total	$ 1,477	$ 1,492	$ 831